1. Field of the Invention
The present invention relates to a heating apparatus which has an electrostatic adsorption function, and specifically to a heating apparatus which has an electrostatic adsorption function used suitably for a heating process of a semiconductor wafer in a production process and an inspection process of a semiconductor device or the like including a process of raising a temperature.
2. Description of the Related Art
Conventionally, a heater around which a metal wire is coiled has been used for heating a semiconductor wafer in a process of production of a semiconductor device. However, when the heater was used, there was a problem of metal contamination to the semiconductor wafer. Therefore, there is proposed use of a wafer heating apparatus united with ceramics which uses a ceramic thin film as a heating layer in recent years (for example, see Japanese Patent Application Laid-open (KOKAI) No. 4-124076).
Among them, when heating a wafer, for example by a molecular beam epitaxy, CVD, sputtering, or the like, it is effective to use a composite ceramic heater consisting of a pyrolytic boron nitride (PBN) and a pyrolytic graphite (PG) with a high purity which does not generate out gas and is excellent in a thermal shock resistance (see Japanese Patent Application Laid-open (KOKAI) No. 63-241921). The heater consisting of such materials has an advantage that it is easily installed compared with a tantalum wire heater which has been used until now, troubles such as thermal deformation, burnout, and short-circuit are not caused, and thus it is easy to use, and comparatively uniform heating is easily achieved since it is an area heater.
Moreover, an electrostatically adsorbing apparatus is generally used for fixing a semiconductor wafer on a heater when heating of a semiconductor wafer in reduced pressure atmosphere, and the material therefor has shifted to ceramics from resins with a tendency of higher temperature process (see Japanese Patent Application Laid-open (KOKAI) Nos. 52-67353 and 59-124140).
Recently, there is proposed a wafer heating apparatus which has the electrostatic adsorption function wherein these wafer heating apparatuses united with ceramics and electrostatically adsorbing apparatus are combined. For example, an apparatus wherein alumina is used for the insulating layer of an electrostatically adsorbing apparatus has been used in a low-temperature region such as an etching process (see New-ceramics (7) p49-53, 1994), and an apparatus wherein pyrolytic boron nitride is used for an insulating layer of an electrostatically adsorbing apparatus has been used in an elevated-temperature region such as a CVD process (see Japanese Patent Application Laid-open (KOKAI) Nos. 4-358074, 5-109876, 5-129210, and 7-10665).
Generally, in such an electrostatically adsorbing apparatus, an electrostatic adsorption power will get strong if a volume resistivity of an insulating layer gets low, for example as indicated in the above-mentioned reference (New ceramics (7), p49-53, 1994). However, the device will be broken due to leakage current if it is too low. Therefore, when an insulating layer is formed in an electrostatically adsorbing apparatus, the insulating layer is formed so that the insulating layer may have a suitable volume resistivity uniformly in a plane by a sintering method, a CVD method, or the like.
Although the electrostatically adsorbing apparatus made of ceramics has been installed in a molecular beam epitaxy apparatus, a CVD apparatus, a sputtering apparatus, or the like as descried above, there have been caused problems of nonuniformity of device characteristics and lowering of yield due to aggravation of a temperature distribution of the electrostatically adsorbing apparatus itself depending on the heat environment to be used, aggravation of a temperature distribution of the wafer itself resulting from contact of gas or plasma to the wafer or the like, with a tendency of higher integration of a semiconductor device in recent years.
Moreover, a so-called single wafer processing in which one wafer is processed at a time is increasingly adopted in a CVD apparatus and a sputtering apparatus, with a tendency of larger diameter of a wafer. As described above, in the case that the wafer with a large diameter is processed, the processing chamber for processing a wafer in a single wafer processing, a cooling system, and a processing gas system are arranged in a concentric configuration centering on the wafer in many cases. Therefore, when a wafer is subjected to heat-treatment, a temperature gradient of the wafer arises in the shape of a concentric circle, and thus some of the heat-treated wafers may have semiconductor device characteristics which are different in the shape of a concentric circle from a center of the wafer. Therefore, the above-mentioned problems, such as uniformity of the device characteristics and lowering of yield are becoming much more serious.